Auxin is critical to plant growth and development, as well as stress responses. Small auxin-up RNA (SAUR) is the largest family of early auxin responsive genes in higher plants. However, the function of few SAUR genes is known owing to functional redundancy among the many family members. In this study, we conducted a phylogenetic analysis using protein sequences of 795 SAURs from Anthoceros angustus, Marchantia polymorpha, Physcomitrella patens, Selaginella moellendorffii, Ginkgo biloba, Gnetum montanum, Amborella trichopoda, Arabidopsis thaliana, Oryza sativa, Zea mays, Glycine max, Medicago truncatula and Setaria italica. The phylogenetic trees showed that the SAUR proteins could be divided into 10 clades and three subfamilies, and that SAUR proteins of three bryophyte species were only located in subfamily III, which suggested that they may be ancestral. From bryophyta to anthophyta, SAUR family have appeared very large expansion. The number of SAUR gene in Fabaceae species was considerably higher than that in other plants, which may be associated with independent whole genome duplication event in the Fabaceae lineages. The phylogenetic trees also showed that SAUR genes had expanded independently monocotyledons and dicotyledons in angiosperms. Conserved motif and protein structure prediction revealed that SAUR proteins were highly conserved among higher plants, and two leucine residues in motif I were observed in almost all SAUR proteins, which suggests the residues plays a critical role in the stability and function of SAUR proteins. Expression analysis of SAUR genes using publicly available RNA-seq data from rice and soybean indicated functional similarity of members in the same clade, which was also further confirmed by qRT-PCR. Summarization of SAUR functions also showed that SAUR functions were usually consistent within a subclade. This study provides insights into the evolution and function of the SAUR gene family from bryophyta to anthophyta, particularly in Fabaceae plants. Future investigation to understand the functions of SAUR family members should employ a clade as the study unit.

中文翻译：

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植物中生长素小 RNA (SAUR) 基因家族的全基因组鉴定和表征：正常生长和胁迫反应期间的进化和表达谱


生长素对于植物生长发育以及应激反应至关重要。小生长素增强 RNA (SAUR) 是高等植物中最大的早期生长素响应基因家族。然而，由于许多家族成员之间的功能冗余，很少有 SAUR 基因的功能是已知的。在本研究中，我们使用来自花角羚、地钱、小立碗藓、卷柏、银杏、买麻藤、毛足安博拉、拟南芥、水稻、玉米、大豆、苜蓿的 795 个 SAUR 的蛋白质序列进行了系统发育分析。 truncatula 和 Setaria italica。系统发育树显示SAUR蛋白可分为10个进化枝和3个亚科，并且3种苔藓植物的SAUR蛋白仅位于第III亚科，这表明它们可能是祖先。从苔藓植物到花植物，SAUR家族出现了非常大的扩张。豆科植物中SAUR基因的数量明显高于其他植物，这可能与豆科谱系中独立的全基因组复制事件有关。系统发育树还表明SAUR基因在被子植物中独立地在单子叶植物和双子叶植物中扩展。保守基序和蛋白质结构预测表明，SAUR蛋白在高等植物中高度保守，几乎所有SAUR蛋白中都观察到基序I中的两个亮氨酸残基，这表明该残基在SAUR蛋白的稳定性和功能中发挥着关键作用。使用公开的水稻和大豆 RNA-seq 数据对 SAUR 基因进行表达分析，表明同一进化枝中成员的功能相似性，这也通过 qRT-PCR 得到了进一步证实。 SAUR 功能的总结还表明，SAUR 功能在一个分支内通常是一致的。这项研究提供了对 SAUR 基因家族从苔藓植物到花植物，特别是豆科植物的进化和功能的见解。未来了解 SAUR 家族成员功能的调查应采用进化枝作为研究单位。